Current TB chemotherapy is incapable of rapidly eliminating one hundred percent of the Mycobacterium tuberculosis bacilli. Although 99% of the bacteria are eliminated within three weeks of commencing treatment, a small population (~ 1%) of drug-tolerant bacilli requires an additional 6-8 months of multidrug treatment to be eliminated. This treatment regimen results in a dramatic improvement in patient health early on and many patients therefore fail to complete the full long-term treatment. This limitation has facilitated te continued emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis strains which have spread globally. The primary goal of this proposal is to more rapidly eradicate drug tolerant bacilli using immunotherapeutic approaches. We believe it is possible to enhance the host's own bactericidal response by using immunotherapy to combat pulmonary immunosuppression. Our preliminary studies indicate that delivery of small interfering RNA [siRNA] transcripts targeting the TGF1 cytokine reduces the pulmonary bacterial load of mice chronically infected with Mycobacterium tuberculosis. Moreover, this effect is enhanced in the absence of the IL-10 cytokine. Here we will test whether siRNA targeting of TGF1 and IL-10 can enhance clearance of drug tolerant bacilli and whether this approach is efficacious in chronic MDR-TB infections. The outcomes will be documented using comprehensive bacteriologic, immunologic, pathologic approaches now routine in our laboratory. We are uniquely equipped with state-of-the-art BSL-III research facilities and have assembled a team of highly experienced researchers with expertise in the fields of mycobacteria infection and RNA regulation in eukaryotic cells. Thus, this application uses innovative, cutting- edge research to develop anti-bacterial products directed against NIAID Category C Priority Pathogens.